Typically heat sinks are mounted to an outer surface of an integrated circuit (I.C.) package to facilitate the dissipation of heat from the integrated circuit contained within the package. Most heat sinks are thermally conductive and have a plurality of extruded fins to provide a large surface area, which allows heat to be more efficiently dissipated by natural or forced convection. Heat sinks are mounted to I.C. packages in variety of ways.
A heat sink may be attached to an I.C. package with a sheet of thermally conductive adhesive film, thermal epoxies, or pre-formed thermal activated epoxy pads which are placed between the flat surface of the package and the heat sink. The adhesive film is then heated while the package and heat sink are pressed together, thereby bonding the package and the heat sink together. Such a solution is characterized by reduced thermal conductivity and migration of the adhesive film over time. Also, different thermal expansion ratios of the heat sink and the package cause mechanical stress on the package. This stress in combination with the curing and hardening required to form the bond leads to decreased mechanical stability of the I.C. package and heat sink assembly. Thus, the heat sink may become loose over time or under shock or vibration. Another drawback to this method of mounting a heat sink to an I.C. package is that the heat sink must be scrapped with the I.C. when the I.C. is bad or otherwise needs to be replaced.
Another heat sink attachment method is to add a stud to the heat spreader on the I.C. package and to screw the heat sink to the package using a nut and washer or other fastening hardware. This method requires a threaded hole in the heat sink and creates a large compression force between the mating surfaces. This assembly torque procedure results in high stresses to both ceramic and plastic packages. This is also generally considered one of the most expensive methods of attachment due to the secondary operations required to manufacture both the heat spreader and the heat sink to accommodate the stud and threaded hole. This assembly process also requires greater quality control to prevent and catch cracked packages during assembly.
There are also a variety of methods known to attach heat sinks to packages by means of spring clamps. These spring clamps generally require a specially designed clamp to be made for each size package, since the clamps are clamped to the package. Also, they either require a specially designed plastic frame to clamp to under the package, which adds to the overall height and weight of the final assembly, or alternatively, they require a special tool for assembly and disassembly which adds to the cost of manufacturing and increases the difficulty of servicing the electronic component.
Accordingly, there is a need in the art of heat sink attachment for an apparatus and method of attachment that is relatively easy to assemble and disassemble, inexpensive, generally generic with regards to package compatibility, and a low profile solution to heat sink attachment.